Identification and medical applications of anti-citrullinated-protein antibodies in rheumatoid arthritis

Abstract

Compositions and methods for detection of anti-citrullinated protein antibodies (ACPAs) in rheumatoid arthritis (RA) patients. Patient samples known or suspected of containing ACPAs were probed against citrullinated proteins, and antibody responses to 190 citrullinated proteins in 20 RA patients were investigated. Unique antibody reactivity patterns in both clinical anti-cyclic citrullinated peptide assay positive (CCP+) and negative (CCP−) RA patients were observed. At individual antigen levels, six novel antibody/antigen complexes were discovered and validated against specific citrullinated antigens (Myelin Basic Protein (MBP), osteopontin (SPP1), flap endonuclease (FEN1), insulin like growth factor binding protein 6 (IGFBP6), insulin like growth factor I (IGF1) and stanniocalcin-2 (STC2)) in RA patients. Identification of immune-dominant epitope(s) for citrullinated MBP was also performed. The identified biomarkers have high specificity, especially MBP.

What is claimed is: 
     
         1 . A composition, comprising an in vitro antigen/auto antibody complex associated with rheumatoid arthritis, wherein said complex includes an antigen selected from the group consisting of one or more of Myelin Basic Protein (MBP), osteopontin (SPP1), flap endonuclease (FEN1), insulin like growth factor binding protein 6 (IGFBP6), insulin like growth factor I (IGF1), and stanniocalcin-2 (STC2). 
     
     
         2 . The composition of  claim 1 , wherein said antigen is Myelin Basic Protein. 
     
     
         3 . A composition, comprising an in vitro antigen/auto antibody complex associated with rheumatoid arthritis, wherein said complex includes reactive epitopes of citrullinated MBP selected from one or more of the sequences MBP N134-C158(HGSKYLATASTMDHARHGFLPRHR DTGILDSIG) (SEQ ID NO. 1) and MBP N144-C176 (DTGILDSIGRFFGGDRG APKRGSGKVSSEE) (SEQ ID NO. 2).